She was elected to Parliament at the 1997 general election for the safe seat of Liverpool Riverside. She held the seat with a majority of 21,799 and has held the seat comfortably at successive general elections. She made her maiden speech on 9 June 1997.[5] When she was re-elected in 2001, the turnout of the vote in her constituency was the lowest in the country at just 34.1%.

She voted "very strongly for" the Iraq War, "very strongly against" an investigation into that war, and "very strongly for" renewal of Trident, Britain's nuclear weapons programme. She is a supporter of gay rights and an opponent of foundation hospitals, the un-elected House of Lords, and fox-hunting.[7] In her time in Parliament she has very rarely voted against the Party line.[8]

She has also played an active role in the effort to pressure the Bulgarian government to free Michael Shields, and recently lobbied for Gillian Gibbons, a teacher jailed in Sudan for blasphemy, who has now been pardoned.

In the 2010 Election campaign, leaflets were distributed in her constituency of Liverpool Riverside targeting Ellman and Luciana Berger for their membership of Labour Friends of Israel and headed "Don't vote for Friends of Israel".[11] A leaflet headed "Remember Gaza" and subheaded "Don't vote for Labour Friends of Israel" was written and widely distributed by Liverpool Friends of Palestine and appears on the website LabourNet.[12][13]

"I am very concerned about antisemitism in the Labour Party. Most members of the Labour Party are not antisemitic but some are", Ellman told Dermot Murnaghan on his Sunday Sky News programme in March 2016. Such people "are being allowed to get away with posting antisemitic comments in their tweets and on their websites."[14] Constituency Labour Party meetings have been tense since the 2015 general election, and comments have been made which Ellman considers antisemitic.[15][16]

Momentum members active in Ellman's constituency allegedly discussed an attempt to deselect her as the seat's Labour candidate at the 2017 election.[17] Ellman believes Momentum are acting as a "party within a party" in her constituency and has advocated an official Labour Party inquiry into the group and intends to resists attempts to deselect her. Corbyn, and those around him, have rejected her assertions.[18]